A mechanical seal provided with an intermediate floating ring has heretofore been used in a machine operated under a high revolutional speed, such as a pump, a compressor and a turbine, in order to decrease the relative sliding speed of the elements concerned. However, in practice, the reduction of the relative sliding speed due to the presence of the intermediate floating ring is only possible when the coefficient of dynamic friction and the coefficient of static friction are at least equal. Since the coefficient of static friction is, in fact, generally larger than the coefficient of dynamic friction, the reduction of the relative sliding speed has not been achieved by the intermediate floating ring of prior art. Thus, the intermediate floating ring has been conveniently utilized merely for the purpose of dissipating generated heat, preventing deformation of the related elements, etc.
Also, it has been devised to provide blades on the outer peripheral surface of the intermediate ring so as to rotate the ring at a preferable range of speed slower than the rotational speed of the shaft by directing the hydraulic force of the lubricating oil or the like to the blades. However, the amount of the lubricating oil to be circulated is determined basically depending on the heat generated by the frictional sliding and, therefore, it would be difficult for such hydraulic force to rotate the intermediate ring at a proper speed overcoming the sliding friction and thus, this approach has not been put into practice.